The spectra of red stars display a complex profusion of atomic and molecular absorption lines and bands. The overlapping of successive absorptions is so severe that the usual methods of temperature measurement cannot be applied. Instead, an indirect procedure has been attempted involving the calculation of a theoretical absorption profile based on a simple model, and comparison with observation. The results show that the detailed stellar profile is relatively insensitive to excitation temperature, so that this particular stellar parameter is relatively uncertain.
John G. Phillips, "The Measurement of the Temperatures of Molecules in Cool Stars," Appl. Opt. 5, 549-553 (1966)